Fix Jest missing webpack config

tests/js/jest.config.json

@@ -15,5 +15,8 @@
     "node_modules/(?!(simple-html-tokenizer)/)"
   ],
   "preset": "@wordpress/jest-preset-default",
+  "transform": {
+    "^.+\\.js$": "<rootDir>/tests/js/jestPreprocess.js"
+  },
   "verbose": true
 }

tests/js/jestPreprocess.js

@@ -0,0 +1,5 @@
+const babelOptions = {
+	presets: [ '@wordpress/babel-preset-default' ],
+};
+
+module.exports = require( 'babel-jest' ).createTransformer( babelOptions );